In the upper incisors, thickness of the enamel layers
appears to vary, with the outer radial enamel forming about 40 percent of the total enamel width in Thomomys, about 25 percent in Cratogeomys, and about 20 percent in Geomys (Figs.
The enamel layer
hardens as the crystallites grow in width and thickness resulting in a mineralised tissue that contains more than 95% mineral by weight.
In the past, scientists had to cut open teeth to count enamel layers
Tallies of enamel layers
that typically form every 7 to 9 days as teeth develop, as well as counts of daily growth bands in the enamel, enabled the scientists to estimate that the child died at age 7 years, 10 months.
Telltale isotopic signatures of carbon from enamel layers
that form sequentially during tooth eruption allowed the team to pinpoint the types of plant materials consumed by the mammals as they ate their way across the landscape through the seasons, according to Eberle.
Some newfound cheek teeth also contain thinner enamel layers
than corresponding teeth from chimps do.